NASA is applying space technology to a decidedly down-to-earth effort that links the production of algae-based fuel with an inexpensive method of sewage treatment.

The space agency is growing algae for biofuel in plastic bags of sewage floating in the ocean.

Jonathan Trent, the lead researcher on the project at NASA's Ames Research Center in California, said the effort has three goals: Produce biofuels with few resources in a confined area, help cleanse municipal wastewater, and sequester emissions of the greenhouse gas carbon dioxide that are produced along the way.

"Algae are the best source of biofuels on the planet that we know about," Trent said in an interview. "If we can also clean [wastewater] at the same time we create biofuels, that would great."

The OMEGA bags are semipermeable membranes that NASA developed to recycle astronauts' wastewater on long space missions. In this case, the membranes let freshwater exit but prevent saltwater from moving in.

Then the algae in the bag feast on nutrients in the sewage. The plants clean up the water and produce lipids – fat-soluble molecules – that will be used later as fuel.

Just as in algae biofuel production on land, the floating OMEGA bags use water, solar energy and carbon dioxide – which in this case is absorbed through the plastic membrane – to produce sugar that algae metabolize into lipids.

Oxygen and fresh, cleansed water are then released through the membrane to the ocean.

The system is foolproof, he said. Even if the OMEGA bags leak, the salty ocean water would kill the algae, preventing the escape of an invasive species.

"Freshwater algae can't compete in the marine environment," Trent said. "We're not putting something out there that could become an invasive species."

And if the wastewater spills, he said, "the only thing we're putting in the water is already in the ocean anyway."

Feasibility

NASA's plastic bags are designed to last up to three years, Trent said. After that, they could be recycled as plastic mulch or chopped and used to improve soil quality and help retain moisture.

"We don't think this would be cost-effective if we just go after the fuels," Trent said. "But we're functioning on at least three different levels: making the products – fuel, fertilizers – then wastewater processing and carbon sequestration. The economic model becomes more reasonable."

In fact, Trent said, the technology is nearly cost-competitive with land-based production methods for algae biofuels that require vast industrial-scale, open-air pond farms or in closed bioreactors.

But land-based methods have limits, Trent said. Open-air ponds and bioreactors gobble up large tracts of land that would be taxed and could potentially compete with agriculture. And even in deserts, where farming is less likely, evaporation of open-air ponds is a threat. Closed bioreactors face similar hurdles. They must be extremely robust in order to hold large amounts of water against air.

Trent envisions the OMEGAs producing enough fuel to fill U.S. aviation needs – 21 billion gallons a year. Doing so would require about 10 acres of ocean, he said.

"It seems huge, but it's a small area in the overall oceans," he said. "And we imagine [the OMEGAs] distributed around, locally distributed ... or franchised and monitored by fishermen."

Hurdles

But the technology faces challenges.

Trent and his fellow researchers are still trying to find plastic capable of withstanding pounding waves and cold temperatures without becoming too brittle for osmosis.

And then there is the matter of money. Venture capitalists are wary, Trent said, but his team has had some luck with the California Energy Commission. A state grant is slated to kick in this August.

The grant should help Trent and the other Ames researchers create a demonstration project within a year. That would let the technology get wider scrutiny and be compared with other renewable-energy technologies.

"On a planet with a population growing at exponential rates and resources dwindling, we're almost in a state of emergency on a timeline measured in decades," Trent said. "I think it's important, this process of coming up with alternatives. ... I don't know if OMEGA is the solution, but it's something that should be carefully scrutinized."

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